This invention relates to fixing device and more particularly to a fixing device for fixing an image formed by electrostatic adhesion of toner particles on a copy sheet by passing such copy sheet through a pair of fixing rollers.
An electrophotographic toner image fixing method which is capable of markedly lengthening the service life of a fixing roller has already been proposed by me in a Japanese Laid-Open Patent Application No. 185544/76. In accordance with this method, a chlorinated silicone oil, fatty acid modified silicone oil, nitrated silicone oil or fluorinated silicone oil may be used as an offset preventing oil, and methylpolysiloxane silicone rubber, vinylpolysilixane silicone rubber or phenylpolysiloxane silicone rubber may be used as a base material layer of the roller. Alternatively, any one of the aforesaid kinds of polysiloxane polymers used as an offset preventing silicone oil may be used as the base material layer of the roller, and any one of the aforesaid kinds of polysiloxane polymers used as the base material layer of the roller may be used as an offset preventing oil.
The method disclosed in this laid-open application has the objects of preventing damage to the roller which may be caused by its swelling due to contact with the oil and preventing the occurrence of an offset phenomenon when fixing of an image is effected. This method has a disadvantage in that the oil does not spread well on the surface of the roller and consequently fixing of an image cannot be effected satisfactorily, because of the fact that the kind of silicone polymer used as an offset preventing oil and the kind of silicone polymer used as the base material layer of the fixing roller are selected in such a manner that they have no affinity with each other so that no swelling of the base material layer of the roller may take place.